Hearing aid amplifier



0d. F, 1941 w! DUBIUER 21,257,840

HEARING AID AMPLIFIER Filed March 15, 1940 Z7 ,8 I .-EARFHONES mlcaopnori g 6 l .L i E E T T T cm J3 b WILLIAM DLJBILIER BY 01 flag ATTORNEY.

F" I G. 5 INVENTOR.

Patented Oct. 7, 1941 UNITED STATES PATENT OFFICE nrzaamo AID AMPLIFiI-Ja William Dubilier, New Rochelle, N. Y.

Claims.

The present invention relates to electron tube hearing aid and similar miniature audio frequency amplifiers for use where space and bulk is at a premium.

Hearing aid amplifiers of known type usually embody one or more electron tubes which require for their operation at least two sources of electric current, one of low voltage (about 1.5 volts) known as "A-battery for heating the cathodes or fers from the disadvantage of assuming largeproportions and bulk if designed for the same period of operation. In practice the size and bulk of the B-battery for the same operating period will be about five or six times the size and bulk of the A-battery thus making the amplifier too heavy and bulky to beconveniently carried in a persons pocket as is desirable in the case'of hearing aid apparatus.

According, an object of the present invention is to substantially overcome the above drawbacks by completely eliminating the necessity of providing a separate B-battery with a minimum of additional elements andv parts required in such a manner as to result in an amplifying apparatus of considerably reducedweight and bulk.

With this object in view, the invention contemplates the provision of simple and efficient means to supply the necessary plate current from a portion of the .A-battery power without substantially decreasing the life of the latter and making necessary frequent replacements. Due to the comparatively low current consumption of the anode circuit of an electron tube as compared with the current consumption of the filament heating circuit, the aforementioned requirement can be easily fulfilled in practice; that is, an eventual slight reduction of the life of the A-battery will be amply offset by a considerable decrease in size and weight of the amplifying apparatus. Moreover, the invention makes it pos- Application March 15, 1940, Serial No. 324,113

(CL'1'l9-107) able anywhere on the market at low costs where- .by more frequent replacements if necessary, say

about each month, would not be feltobjectionable both from a point of view of convenience and cost. In this respect the invention presents an added advantage compared with the known hearing aid amplifiers requiring special and comparatively heavy B-batteries usually available from specified manufacturers only and frequently resulting in lack of supply possibilities to the great discomfiture and inconvenience of persons afllicted with bad hearing.

v Accordingly the invention involves in general the provision of a converting device in the form of an electromagnetic vibrator or interrupter .serving to open and close a current drawn from the A-battery serving to supply the plate potential for the tubes, whereby this vibrator is designed and adjusted to have a vibrating or interrupting frequency which is high compared with the highest audible frequency or limit of hearing at least as far as the person is concerned for whose use the amplified is destined. A safe average limit for a majority of persons suflering a comparatively slight hearing loss is about 5000 cycles. This value may, however, be substantial-- 1y less in more serious cases of hearing loss where the limit frequency has a substantially lower value:

The interrupted current of low voltage (1.5 volts) according to one embodiment of the invention is applied to a small transformer and stepped up to the required high voltages (about volts) for supplying the plate or space current of the amplifying tubes. The outer current oil. the transformer which is an alternating current according to a further feature of-the invention is sible to more frequently renew the batteries by enabling the use of simple batteries of the standard type as used in flash-lights or the like availdirectly used for supplying the plate potential for the tubes, 1. e. only thepositive half waves of the current will be utilized and cause successive intermittent operating or conducting cycles for the tubes. Due to the fact that the interrupting or vibrating frequency is chosen to be above audibility the intermittent operation of the tubes will not result in any audible interference or impairment of the fidelity of the sound currents supplied by the output of the amplifier and serving to energize the ear-phones of the hear aid device.

An interrupter or electromagnetic vibrator operating at super-audible frequency and associate transformer can be easily made with very small dimemions and weight compared with the were used.

Further details and advantages of the invention will become more apparent from the follow-' form of a practical lay-out of a hearing aid amplifier constructed in accordance with the invention.

Figure 6 is a schematic view illustrating a modified vibrating system according to the invention. and

Figure "I shows a curve illustrative of the function of Figure 6.

Like reference characters identify like parts in the diflerent views of the drawing.

Referring to Figure 1, there is shown a vibrating converter for changing low voltage direct current into high voltage alternating current for use as a plate supply in hearing aid or similar miniature amplifiers and comprising a source of low voltage direct potential shown at It such as a dry battery exciting an electromagnetic vibrator, the latter comprising an iron-core magnet coil ii, a vibratory contact l2 resiliently mounted upon a fiat spring I! or the like cooperating with a fixed contact ll. In the closed condition of the contacts I! and ii the current of the battery ID will flow through the coil ii, contact l2. contact ii. the primary winding of a transformer i5, and back to the-battery by wayof switch i1. As a result of the current flow upon closing the switch H, the iron core of coil ii will attract contact I! thereby opening the circuit. This in turn will cause the contact l2 to engage again contact I: due to the resiliency of the spring i2, thereby repeating the cycle and resulting in a periodic opening and closing of the circuit at a frequency which is mainly determined by the resiliency of the spring I! and its initial bias adjusted by the aid of a set screw or the like adapted to change the position bf contact i 3 as shown in greater detail in Figure- 2 to be described presently. In order to reduce sparking and arcing between the contacts i2 and it, there is provided a condenser IS in shunt relation to'the contact and connected in the example shown between the lower end of spring I! and the lower end of the primary winding of the transformer IS. The design and adjustment of the contacts is such that the vibrating or interrupting frequency is above audibility as pointed out hereinabove. This can be easily accomplished by using the proper materials and thickness for the contact spring [2 and by suitably initially biasing the spring i2. Due to the relatively high vibrating frequency required, the dimensions of the vibrating parts as well as the magnet coil can be kept within very small limits whereby the entire device can be reduced to a very small size and weightcompared with a B-battery required in amplifiers heretofore known in the art.

Referring to Figure 2, there is schematically shown one form of aconstructionai embodiment of a vibrating device on an enlarged scale. Ex-' periments have shown that the actual size of the vibrator may be as small as about one-third or less than the dimensions shown in the drawing. The entire vibrating structure is suitably mounted in an evacuated receptacle such as a glass tube or bulb '2. The latter is formed at its lower end with a re-entrant portion terminating in a press 33. The tube is suitably mounted in a base 34 in a manner similar to vacuum tubes of known construction. Item 35 represents a U-shaped iron core for the vibrat ing magnet, being preferably of laminated construction and having a magnet winding 38 wound about the yoke of the core. The vibrating contact 31 opposite one leg of the magnet core 35 is suitably affixed to one end of a leaf spring 38 which has its opposite end secured to the other leg of the magnet core. Item 39 is a U-shaped bracket formed by bending a flat metal strip encircling the contact 31 and having its legs fixedly secured to the opposite faces of the magnet core 3!. The bracket 38 carries the cooperating contact 40 which can be adjusted relative to the contact 81 by the aid of a set screw 40' for initially biasing the spring II. The entire magnet structure is suitably mounted upon a base plate I! such as by means of supporting brackets 42 and II. In assembling the device, the magnet structure is first mounted upon the plate or mounting disc 43 and inserted into the tube 12 with the disc resting against the lower bead or shoulder'of the tube. Electrical connectors passing from the prongs a, d. c at the base It through the press a are then connected to the elements of the vibrator in the manner shown in Figure 1 by soldering, welding or in any other manner. A further mounting disc ll resting against the upper bead or shoulder of the tube 32 may be provided to provide added mechanical rigidity. Thereupon,

the tube is exhausted to expel air and moisture, and sealed. Thus, the vibrator will operate in a vacuum and deterioration of the contacts by oxidation will be substantially avoided. In this manner the vibrator will function permanently without substantially requiring readjustment or resetting of the contacts. Alternatively, the tube may be filled with an inert gas to maintain the operating stability and prevent an early deterioration of the contacts. In order to suppress any residual arcing or sparking between the contacts, condenser i6 may be suitably mounted within the base 34 and electrically connected to the circuit in the manner shown in Figure 1.

Referring to Figure 3, there is shown a complete three-stage hearing aid amplifier com prising a microphone, preferably a crystal microphone, shunted by a resistance 2| coupled to the grid and cathode of an input tube 22 of any desired type and design known in the art. The second and third amplifying stages comprise similar tubes 23 and 25 with resistance coupling networks 25 and 28 connecting the output of one stage to the input of the succeeding stage in a manner well understood by those skilled in the art. The output of the last tube 2| is applied to an ear-phone 28 by way of audio frequency transformer 21. A battery l0 serves to supply the heating current for the filaments of all three tubes connected in series while the plate current is supplied from the secondary of a transformer I! connected to the output of the converter ll of substantially the same type and energized from the battery I! as described in Figures 1 and 2. The remaining parts such as screen grid resistors, by-pass condensers, etc., are of standard design and need not be discussed as they form no part ofthe present invention.

Referring to Figures 4 and 5. the former showing a side view and the latter showing a top view in schematic form of a hearing aid amplifier in approximately natural size, item ll represents a casing of insulating material such as a molded casing of artificial resin being divided into compartments by partition walls It and 82. One of the compartments serves to house three batteries 52 of standard size as used in flashlights and the like, each having about a" diameter and 2" length. If a circuit according to Figure 3 is used the batteries are connected in series whereby each of the filaments of tubes 22 to 25 is heated to the proper emitting temperature. The wall 52 serves as a support or chassis for the amplifying tubes 22, 23 and 24 while a further mounting plate or chassis ll is provided to support the vibrator I, a pair of transformers 51, ll corresponding to transformers l4 and 21, Figure 3, respectively, as well as the remaining parts of the circuit such as resistors and condensers suitably arranged within the space available and connected in the manner shown in Figure 1.

Referring to Figure 6 there is shown a simplifled vibrating system according to the invention designed to dispense with a special output transformer. According to this embodiment, the circuit elements, in particular the magnet coil H, are designed in such a manner that the inductive voltage peak at the instant of interruption of the contacts I2 and is known as an inductive kickback supplies suificient high voltage power to. enaple proper function of the amplifier. As is understood in this case itis advantageous to design the device in such a manner that the vibrating frequency or sequence of the plate voltage peaks is as high as possible, which may be substantially above the limit of audibility to insure sufficient power supply to the plate circuit to afford eflicient operation of the amplifier.

The operation of Figure 6 will be further understood by reference to Figure 7 wherein the current through the vibrating circuit is plotted as a function of time. At the instant A, the contacts i2 and i3 are closed whereby the current starts to increase from zero according to an exponential relationship determined by the circuit constants to a value B at the instant of separation or interruption of the contacts. Due to the magnetic energy stored in the coil II, a high inductive peak voltage 13 is induced in the winding H whose value may be many times the value of the input voltage of the battery and may serve to energize the plate "circuit of the amplifier. Due to the sharply peaked character of this voltage, a high pitched hiss may occur in the ear-phone connected to the output of the amplifier. Such a hiss, as experience has shown, does not constitute a drawback but has been found to be beneficial in sharpening or increasing the sensitivity of hearing.

It will be evident from the foregoing that the invention is not limited to the specific constructions and arrangements of parts and circuits shown and described herein for illustration but that the principle underlying the invention is susceptible of modifications and variations coming within the broader scope and spirit of the invention as defined in the appended claims. I

The specification and drawing areaccordingly to be regarded in an illustrative rather than a limiting sense.

I claim:

1. The combination with a wearable hearing aid device for use where the loss in amplitude response is accompanied by a substantial deficiency with respect to the audible noteswithin a partial range of the normal audible sound spectrum, of an electron tube amplifier for raising the sound amplitude, said amplifier requiring cathode heating current of relatively low voltage and anode operating current of relatively high voltage, a source of low voltage direct current, means for directly drawing cathode heating current from said source, and further means for deriving anode operating current from said source including a vibrating device for periodically interrupting a fractional current drawn from said source at a frequency within the deficiency range of the ear for which the device is destined, means for stepping up the voltage of the interrupted current impulses, and means for directly utiliz ng the stepped-up voltage impulses as anode operating voltage for said amplifier.

2. The combination with a wearable hearing aid device for use where the loss in amplitude response is accompanied by a deficiency with respect to the audible notes within a partial range of the normal audible sound spectrum, of an electron tube amplifier for raising the sound amplitude, said amplifier requiring cathode heating current of relatively low voltage and anode operating current of relatively high voltage, a source of low voltage direct current, means for directly drawing cathode heating current from said source, and further means for deriving anode operating current from said source including an electro-mechanical vibrator for interrupting a partial current drawn from said source at a frequency within the deficiency range of the ear for which the device is destined, a transformer for stepping up the interrupted current into a high voltage impulse current, and means for directly utilizing said impulse current as anode operating voltage for said amplifier.

3. The combination with a wearablehearing aid device for use where the loss in amplitude response is accompanied by a deficiency with respect to the audible notes within a partial range of the normal audio sound spectrum, of an electron tube amplifier for raising the sound amplitude, said amplifier requiring cathode heating current of relatively low voltage and anode operating current of relatively high voltage, a source of low voltage direct current, means for directly drawing cathode heating current from said source, and further means for deriving anode operating current from said source including a circuit for drawing a partial direct current from said source, an induction coil and a vibrator inserted in said circuit for interrupting the current drawn at a frequency within the deficiency range of the ear for which the device is destined, said induction coil being adapted to produce a series of self-induced high voltage impulses suitable for directly supplying anode operating voltof an electron tube amplifier for raising the sound amplitude, said amplifier requiring cathode heatins current of relatively low voltage and anode operating current of relatively high voltage, a source of low voltage direct current, means for directly drawing cathode heating current from said source, and further means for deriving anode operating current from said source including a circuit for drawings partial direct current from said source, an induction coil and an electromechanical vibrator inserted in said circuit for interrupting the current drawn at a frequency within the deficiency range of the ear for which the device is destined, said induction coil being adapted to produce a series oi self-induced high voltage impulses suitable for directly supplying anode operating voltage to said amplifier.

5. The combination with a wearable hearing aid device for use where the loss in amplitude response is accompanied by a deficiency with respect to the audible notes within a partial range of the normal audible sound spectrum, of an electron tube amplifier for raising the sound amplitude, said amplifier requiring cathode heating current of relatively low voltage and anode operating current of relatively high voltage, a source of low voltage direct current, means for directly drawing cathode heating current from said source, and further means for deriving anode operating current from said source, including a circuit for drawing a partial direct current from said source, an induction coil and an electro-mechanical vibrator mounted in an evacuated space inserted in said circuit for interrupting the current drawn at a frequency within the deficiency range of the ear for which the device is destined, said induction coil being adapted to produce a series of self-induced high voltage impulses suitable for directly supplying anode operating voltage to said amplifier.

8. The combination with a wearable hearing aid device for use where the loss in amplitude response is accompanied by a substantial deiiciency with respect to the audible notes in the higher frequency range of the normal audible sound spectrum, of an electron tube amplifier for raising the sound amplitude, said amplifier requiring cathode heating current of relatively low voltage and anode operating current of relatively high voltage, a source oi low voltage direct current, means for directly drawing cathmtle heating current from said source, and further means for deriving anode operating current from said source including a vibrating device for interrupting a partial current drawn from said source at a frequency above the audible limit of the ear for which the device is destined, means for stepping up the voltage of the interrupting current impulses, and means for directly using the steppedmp voltage impulm as anode operating voltage for said amplifier.

7. The combination with a wearable hearing aid device for use where the loss in amplitude response is accompanied by a substantial deficiency with respect to the audible notes in the higher irequency range of the normal audible sound spectrum, an electron tube amplifier for rais= ing the sound amplitude, said amplifier requiring cathode heating current of relatively low voltage and anode operating current of relatively high voltage, a source of low voltage direct current, means for directly drawing cathode heating current from said source, and humor means for deriving anode current from said source including acsmso current drawnfrolnsaideouroeatafrequency abovetheaudiblelimitoftheearforwhiehthe device is destined, a transformer for topping up the interrupted current to ahighvoltage alternatingcurrent,andmeansfordiroctlyutiliaing said alternating current as anode operating voltage for said amplifier.

8. The oombinaflon with a wearable hearing aiddeviee forusewherethelolsinamplihide response is accompanied by a substantial deficiencywithmttotheaudiblenotesinthe higher frequency range 0! the neural audible sound spectrum, of an electron tube amplifier for raising the sound amplitude, said amplifier requiring cathode heating current of relatively low voltage and anodeoperating current oi relatively high voltage, a source of low voltage direct current, means for directly drawing cathode heating current from said source, and further means for deriving anode current fromsaid source including a circuit for drawing a fractional direct current from said source, an induction coil and a vibrator inserted in said circuit for interrupting the current drawn at a frequency above the audible limit of the ear for which the device is destined, said induction coil being adapted to produce a series of self-induced high voltage impulses suitable for directly providing anode operating voltage for said amplifier.

9. The combination with a wearable hearing aid device for use where the basin amplitude response is accompanied by a substantial deficiency with respect to the audible notes in the nigher frequency range of the normal audible sound spectrum, of an electron tube amplifier for raising the sound amplitude,- said amplifier requiring cathode heating current of relatively low voltage and anode operating current of relatively high voltage, a source of low voltage direct current, means for directly drawing cathode heating current from said source, and further means for deriving anode current from said source including a circuit for drawing a fractional direct current from said source, an induction coil and an electromechanical vibrator inserted in said circuit for interrupting the current drawn at a frequency above the audible limit of the ear a vibrating device ior interrupting a fractional for which the device is destined, said induction coil being adapted to produce a series of self-in duced high voltage impulses suitable for directly groviding anode operating voltage for'said ampli- 10. The combination with a wearable hearing aid device for use where the loss in amplitude response is accompanied by a substantial deficiency with respect to the audible notes in the higher frequency range of the normal audible sound spectrum, of an electron tube amplifier for raising the sound amplitude, said amplifier requiring cathode heating current of relatively low voltage and anode operating current of relatively high voltage, a source of low voltage direct current, means for directly drawing cathode heating current from said source, and further means for deriving anode current from said source including an electromechanical vibrator mounted in an evacuated space for interrupting a fractional current drawn from said source at a frequency above the audible limit of the ear for which the device is destined, a transformer for stepping up the interrupted current to a high voltage alternating current, and means for directly utilizing said alternating current as anode operating voltage for said amplifier;-

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